1. Field of the Invention
The present invention relates to a system for controlling backlight that is used together with a liquid crystal display panel, and in particular, relates to a system that is used for small displays.
2. Description of Related Art
Backlight modules that use a compound semiconductor light-emitting element such as a light-emitting diode in place of a fluorescent tube have become popular in recent years. Such a module normally uses light-emitting diodes of three colors, red (R), green (G), and blue (B). Mixtures of these colors are introduced into a light guide member disposed at the back surface of a liquid crystal panel. The light guide member supplies illuminating light from the back surface side of the liquid crystal display surface. Backlight modules wherein light-emitting diodes serve as the light source have advantages, including the fact that color reproducibility is better than that obtained when a fluorescent tube is used, and the use of these backlight modules promises to increase.
Many control systems for such backlight modules comprise a feedback mechanism. That is, the intensity of each component for each color of mixtures of the red, green, and blue light that form the backlight is detected by a light sensor or detector. The intensity signals of each color that has been detected are fed back to a control circuit for controlling the light emission from each of the light-emitting diodes. The control system applies a predetermined compensation to the emission intensity of each light-emitting diode based on reference signals that are set by the user or that have been initially set. The theory behind this type of system is, for instance, described in JP National Publication of International Application (Kohyo) 2002-533,870; Unexamined Japanese Patent Application (Kokai) 2001-92,414; Unexamined Japanese Patent Application (Kokai) 2001-332,764; and Unexamined Japanese Patent Application (Kokai) 2004-29,141
By means of this type of system, the light sensor can be disposed adjacent to the light-emitting diode, but it is preferred that light be detected near the liquid crystal panel module. In the latter case, a light sensor for backlight in a conventional, relatively large display is disposed joined with the light guide member such that light can be efficiently received. Similar technology is described in Unexamined Japanese Patent Application (Kokai) 2004-170,721.
The above-mentioned system must be such that it can also be used in relatively small backlight modules. Nevertheless, in this case, the light guide member for introducing backlight that is disposed on the back surface of the liquid crystal module is as thick as 1 mm. Consequently, the light sensor cannot be disposed with stability on the side end face of the light guide member. Furthermore, even if it is temporarily disposed at the side end face, the light guide is thin in comparison to the light-receiving part and light therefore cannot be introduced to the light sensor efficiently, or the structure becomes one where the light sensor projects from the light guide to the base side and it therefore does not satisfy the requirement of miniaturization.
Therefore, an object of the present invention is to provide an improved structure for a backlight module control system that can even be used for small, thin display devices.